Temperature and enrichment are predicted to have dramatic impacts on food-webs
Stability is theoretically predicted to have an U-shape with temperature (Uszko et al. 2017), higher temperature leading to higher stability in “cold” food-webs, and to lower stability in “hot” food-webs
Futhermore, metabolic theory predicts that higher trophic level suffer most from high temperature. Metabolic costs increase exponentially with temperature and higher trophic levels have generally higher body mass and then higher basal metabolic cost
Enrichment (measured here by DBO), is predicted to decrease stability by increasing the amplitude of population fluctuations (Rosenzweig 1971)
Insterestingly, enrichment is predicted to dampens the effect of high temperature by increasing resources thereby decreasing starvation risk due to high temperature (Tabi, Petchey, and Pennekamp 2019)
Stream and lakes are really different ecosystems:
Develop hypothesis:
\(N_i = \alpha + \beta_0F + \beta_1T_i + \beta_2T_iF + \beta_3D_i + \beta_4D_iF + \beta_5D_iT_i + \beta_6D_iT_iF + \epsilon\)
We certainly need to assess the collinearity among network descriptors in the SEM, it may be high, but it was ok in (Danet et al. 2021).
Due to biological and environmental data availability, the temporal coverage is from 2005 to 2017.
256 sampled lakes (with a total of 397 obs) and 373 sampled stream stations (with a total of 2,791 obs) were considered.
| variable | mean | sd | median | min | max | mean | sd | median | min | max |
|---|---|---|---|---|---|---|---|---|---|---|
| dbo (mg/L) | 1.5 | 0.9 | 1.3 | 0.5 | 5.5 | 1.7 | 0.6 | 1.6 | 0.5 | 4.9 |
| temperature (°C) | 13.9 | 1.9 | 13.9 | 6.0 | 18.6 | 11.6 | 1.8 | 11.6 | 1.8 | 17.8 |
| metric | mean | sd | median | min | max | mean | sd | median | min | max |
|---|---|---|---|---|---|---|---|---|---|---|
| connectance | 0.1 | 0.0 | 0.1 | 0.1 | 0.2 | 0.2 | 0.0 | 0.2 | 0.1 | 0.2 |
| max trophic level | 4.0 | 0.1 | 4.0 | 3.2 | 4.5 | 3.8 | 0.2 | 3.8 | 2.9 | 4.4 |
| mean trophic level | 3.3 | 0.2 | 3.3 | 2.6 | 4.1 | 3.5 | 0.3 | 3.5 | 2.5 | 4.2 |
| number of nodes | 36.4 | 8.7 | 36.0 | 10.0 | 64.0 | 31.9 | 15.0 | 30.0 | 8.0 | 92.0 |
| richness | 9.2 | 2.5 | 9.0 | 1.0 | 18.0 | 7.6 | 5.0 | 7.0 | 1.0 | 25.0 |